In vivo analysis of cell proliferation and apoptosis in the CNS.

The balance between cell proliferation and death is fundamental in several morphogenetic processes and ultimately determines the mass, shape and function of the various tissues and organs that form the animal body. Apoptosis is a gene-regulated process of programmed cell death (PCD) that plays fundamental roles in several normal and pathological conditions. This form of "cell suicide" is most often found during embryonic development, but also in normal cell and tissue turnover. Although the nervous tissue is traditionally regarded as being fundamentally constituted by post-mitotic non proliferating cell, analysis of cell proliferation and apoptosis in vivo has recently gained an increasing importance mainly considering that: i. proliferative and/or apoptotic events have been extensively characterized not only during embryonic development but also in several areas of the post-natal and adult brain, ii. trophic factor deprivation often results in apoptotic cell death of target neurons, and, iii. links have been hypothesized between apoptosis and signal transduction. We describe here a series of techniques that are currently employed in our laboratory for the detection of proliferating and apoptotic cells in the central nervous system (CNS) directly on tissue sections both at light and electron microscopic level. We will also briefly consider some biochemical assays which may be of relevance for a more in depth characterization of the apoptotic process in neural cells.